A method for producing a conjugated diene such as butadiene and the like by subjecting a monoolefin such as n-butene and the like to an oxidative dehydrogenation reaction in the presence of a catalyst is conventionally known.
This reaction proceeds according to, for example, the following reaction formula, and water is formed as a by-product.C4H8+½O2→C4H6+H2O
As a production catalyst of butadiene through a representative oxidative dehydrogenation reaction of n-butene, there is a metal oxide catalyst containing molybdenum. For example, Patent Document 1 describes a complex metal oxide catalyst containing silica as well as at least one member of molybdenum, iron, nickel, and cobalt.
The metal oxide catalyst containing molybdenum is also used on the occasion of obtaining an unsaturated nitrile such as acrylonitrile and the like by allowing propylene to react with ammonia and oxygen by an ammoxidation method. However, Non-Patent Document 1 describes that water and a molybdenum compound react with each other to form a volatile molybdenum hydrate, and there is a concern that volatilized molybdenum deposits in a cooling pipe or the like within a reaction apparatus, thereby eroding a quality of the material. Accordingly, Patent Document 2 describes that by constituting a reaction apparatus using a material having a standard electrode potential of oxidation reaction in an aqueous solution system of −0.2 V or more and not more than 2.8 V, adhesion of the molybdenum compound can be suppressed.